It depends on the specific uses. In some food, the alternatives can be sorbitol and glycerol, as both can be used as humectants.

Is it vegan?

Yes, propylene glycol made from the above three manufacturing processes are all vegan as without using animal-derived products, so it is suitable to the diet of vegetarians.

Is it gluten free?

Yes, propylene glycol is gluten free as without wheat, rye, barley, or crossbreeds of these grains.

Conclusion

Now you may have a knowledge of the humectant & solvent carrier – Propylene Glycol (E1520), from the following aspects:

Three manufacturing processes.

Uses in food, animal pets, cosmetics and antifreeze & coolant.

Safety

FAQs 

What kinds of food labels have you found this ingredient in? Or if you have any questions or remarks about this additive, feel free to let me know in the comments.

http://www.chinafooding.com/Propylene_Glycol